The primary goal of this research is to gain a better understanding of the physiological mechanisms underlying the hormonal control of behavior. The behavioral actions of androgens such as testosterone appear to be mediated by the interaction of their estrogenic and androgenic metabolites. Both androgenic and estrogenic metabolites are necessary to activate normal male behavior patterns in a variety of species. The major focus of the present research is to determine how these two classes of hormones interact within the brain to elicit such behaviors. Activity of enzymes responsible for the synthesis and degradation of acetylcholine and monoaminergic neurotransmitters, as well as levels and turnover of serotonin will be monitored in specific brain nuclei known to mediate behavior dependent on the combined actions of estrogenic and androgenic metabolites. Examining the responses of these neurotransmitter systems lo treatment with androgens alone, estrogens alone, or combined treatment with androgens + estrogens should help us to understand how these two classes of hormones interact in the brain to modulate behavior. These hormone treatments have already been shown to affect catecholamine levels and turnover in these nuclei. To further explore this effect, catecholaminergic cell bodies will be located, and the ability of the three hormone treatments to induce de novo synthesis of the rate-limiting enzyme in catecholamine synthesis determined. A second line of research investigates the mechanism underlying the ability of a 5 alpha-reduction blocker to greatly enhance the ability of aromatizable androgens to activate behavior. A third line of research investigates the source of estrogens found in the bloodstream and will determine if plasma estrogen levels measured by RIA are correct. This research on hormone interactions in the central nervous system, the specificity of hormone-sensitive neural mechanisms, and hormone metabolism should increase our understanding of the organization and functioning of endocrine control mechanisms. Hopefully, it will also contribute to the improve management of endocrine function.